The present invention concerns an indicator device for providing a visual signal to a tool operator to assure the tool operating axis is perpendicular to the surface of a work piece.
In certain types of fabrication work it is desirable that pilot holes for fasteners be formed truly perpendicular or normal through the pieces being joined. Pilot holes inclined to a desired axis incur wasted man hours spent trying to remedy same by re-drilling the work pieces or beveling a shim. Installation of a metal fastener other than in normal disposition to the joined pieces may impart asymetrical loads to the fastener causing premature failure of same.
The problem of boring pilot holes normal to a work piece surface is entirely distinct from boring pilot holes along vertical or horizontal axes. In the prior art are gravity responsive drill attachments such as shown in U.S. Pat. Nos. 4,141,151 and 4,189,726. A pilot bore drilled with such an aid would be perpendicular to the work piece surface only if the surface is truly vertical or horizontal which is seldom the case in certain types of fabrication, e.g., airframe.